This description relates to a composite shroud hanger assembly, and, more particularly, to a method and system for a two-piece ceramic matrix composite (CMC) shroud hanger assembly which clamps across a forward vertical wall of a shroud to support the shroud while transferring turbine nozzle load through the shroud hanger assembly and into a gas turbine engine casing.
At least some known gas turbine engines include a core having a high pressure compressor, combustor, and high pressure turbine (HPT) in serial flow relationship. The core engine is operable to generate a primary gas flow. The high pressure turbine includes annular arrays (“rows”) of stationary vanes or nozzles that direct the gases exiting the combustor into rotating blades or buckets. Collectively one row of nozzles and one row of blades make up a “stage”. Typically two or more stages are used in serial flow relationship. These components operate in an extremely high temperature environment, and may be cooled by air flow to ensure adequate service life.
Components of the gas turbine engine, for example stationary shrouds or shroud segments and their supporting structures, such as, shroud hanger assemblies, are exposed to a heated stream of combustion gases. It is desirable to operate a gas turbine engine at high temperatures most efficient for generating and extracting energy from these gases. However, such elevated temperatures frequently exceed the temperature capability of the basic component materials and can result in compromise of mechanical and/or physical properties, or distortion of the components. Consequently, use has been made of various heat-resistant coatings and/or cooling processes. If cooling is used, is it usually implemented by channeling relatively cooler air, for example from various points in the high-pressure compressor of the engine, and discharging it within or from a component to provide convection, impingement, or film cooling.
In other examples, due to operating temperatures within the gas turbine engine, materials having a low coefficient of thermal expansion (CTE) are used. For example, to operate effectively in such adverse temperature and pressure conditions, ceramic matrix composite (CMC) materials may be used. These low coefficient of thermal expansion materials have higher temperature capability than similar metallic parts, so that, when operating at the higher operating temperatures, the engine is able to operate at a higher engine efficiency. However, such ceramic matrix composite (CMC) have mechanical properties that must be considered during the design and application of the CMC. CMC materials have relatively low tensile ductility or low strain to failure when compared to metallic materials. Also, CMC materials have a coefficient of thermal expansion which differs significantly from metal alloys used as restraining supports or hangers for CMC type materials. Therefore, if a CMC component is restrained and cooled on one surface during operation, stress concentrations can develop leading to a shortened life of the segment.
At least some known gas turbine engine are manufactured using a CMC “open shroud” configuration, which may be preferred for manufacturing over other types of segmented CMC shrouds, such as a “box shroud”. Complex hanger assemblies have been required, however to transfer a load from, for example, a nozzle of a turbine through the shroud hanger assembly without damaging the shroud. Because of the configuration, some portions of the CMC components are not always in compression. CMC material can withstand compression loads, but experiences a reduced life when subject to tensile or moment loads.
Other hanger designs have used a flexible spring-arm at the forward or aft side of the hanger and a ridged arm at opposite side to provide a light clamp load across the entire shroud for sealing. At the same time, additional engine components or more complex hanger designs were used to transfer the nozzle load around the shroud and through the hanger and into the turbine casing.